The Hickory Sandstone is Late Cambrian in age and overlies unconformably the Precambrian Town Mountain Granite. The basal contact has a local relief of between 20 and 40 ft (6 to 12 m) as indicated by the surface topography of recently exhumed granite exposed approximately 1 mile (1.6 km) to the southwest of the study area. Locally, the relief on the contact is in excess of 40 ft (12 m).

The Hickory Sandstone is a member of the Riley Formation and locally is approximately 450 ft (137 m) thick. It is the basal unit of a major transgressive sequence and consists of nonmarine braided stream deposits that grade upward into shallow marine deposits. Several models have been proposed for the details of the depositional environments. Stratigraphic evidence suggests a subsequent maximum depth of burial of about 1 km.

For field mapping purposes, the Hickory Sandstone is divided into three subunits: the lower, middle, and upper Hickory Sandstone. Based on core data obtained during the IAP pilot study, the middle Hickory is further subdivided into two subunits. The following generalized descriptions are based on both field and core observations. Color figures of representative core sequences of each unit of the Hickory are included in the Pilot Study.

The lower Hickory Sandstone is a 200 ft (61 m) thick, buff to yellow-brown, medium- to very coarse-grained, poorly-sorted, friable to weakly-cemented, nonfossiliferous, quartzose to subarkosic sandstone with widely-spaced, thin, clay-rich interbeds (Figure, 149K). Large festoon crossbedding is common. The frequency of silt and clay-rich interbeds increases upward.

The middle Hickory Sandstone is 200 ft (61 m) thick and, based on relative frequency of clay-rich interbeds, consists of two subunits. The lower unit, subunit 1, is 115 ft (35 m) thick and consists of fine to coarse, fair to moderately well sorted, thin- bedded, quartzose sandstone with frequent clay-rich laminae and interbeds (Figure, 139K). Bioturbation is common. Thicker clay-rich interbeds are laterally extensive. Subunit 2 is 85 ft (26 m) thick and consists of medium to coarse, generally well rounded, poorly sorted, fossiliferous, sandstone that becomes progressively more hematitc upward (Figure, 156K). Clay-rich interbeds occur but are much less frequent than in subunit 1. Intraformational conglomerates occur in both subunits of the middle Hickory.

The upper Hickory Sandstone is a 50 ft (15 m) thick, red to maroon, coarse-grained, rounded, moderately well-sorted, fossiliferous quartz sandstone with iron-oxide ooids and cement with some interbeds of fine grained, quartzose sandstone and shale (Figure, 139K).